Alexander Duane's outstanding contribution to the understanding of motor anomalies has been his demonstration that the relationship between the amounts of deviation for distance and for near is of diagnostic importance. Observing that the variations in this relationship took a definite pattern, he formulated a method of classification that has withstood the test of time. He placed cases of esotropia that were greater for distance than for near into a heterogeneous group, which he called "divergence insufficiency." A great many patients within this group also had vertical deviations. The importance of the vertical deviations were recognized by Duane when he stated1:
Uncomplicated idiopathic divergence insufficiency is a comparatively rare condition and moreover some of the cases that would seem to fall in this category are probably secondary to some disorder of the vertical muscles (elevators or depressors).
When the attempt was made to classify cases of esotropia in the
URIST MJ. Esotropia with Bilateral Depression Adduction in ^/waauciion. AMA Arch Ophthalmol. 1956;55(4):509–515. doi:10.1001/archopht.1956.00930030513008
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